Organic Molecules: Lipids

• Hydrophobic organic molecules

• More calories per gram than carbohydrates.

• Four primary types:– fatty acids– triglycerides– phospholipids– steroids

Fats are macromolecules constructed from:

• Glycerol, a three-carbon alcohol.

• Fatty acids *Composed of a carboxyl group at one end and

an attached hydrocarbon chain (“tail”).

* Carboxyl group (“head”) has properties of an

acid.

* Hydrocarbon chain – long carbon skeleton.

Non-polar C-H bonds make the chain

hydrophobic and not water soluble.

Fatty Acids

• Chain of usually 4 to 24 carbon atoms

• Carboxyl (acid) group on one end and a methyl group on the other

• Polymers of two-carbon acetyl groups

Fatty Acids• Saturated fatty acid - carbon atoms saturated

with hydrogen • Unsaturated fatty acid - contains C=C bonds

that could bond more hydrogen

Triglyceride Synthesis (1)• Three fatty acids bonded to glycerol by

dehydration synthesis

Triglyceride Synthesis (2)

• Triglycerides are called neutral fats– fatty acids bond with their carboxyl ends, therefore no

longer acidic

Triglycerides

• Hydrolysis of fats occurs by lipase enzyme

• Triglycerides at room temperature– liquids called oils, often polyunsaturated fats from

plants– solids called fats, saturated fats from animals

• Function - energy storage– also insulation and shock absorption for organs

Phospholipids

• Composed of a hydrophilic “head” attached to two fatty acids.

• Third fatty acid is replaced with a negatively charged phosphate group.

• Can have small variable molecules (usually polar or charged) attached to phosphate.

A Phospholipid - Lecithin

Phospholipids• Cluster in water as their hydrophobic tails

turn away from water (micelle formation).

• Major constituents of cell membranes.

Steroids• Cholesterol

– other steroids derive from cholesterol• cortisol, progesterone, estrogens, testosterone and

bile acids

– is an important component of cell membranes – produced only by animals

• 85% naturally produced by our body • only 15% derived from our diet

Cholesterol

• All steroids have this 4 ringed structure with variations in the functional groups and location of double bonds

Cholesterol – LDL vs. HDL

• LDL: “Bad” cholesterol– Low-density Lipoprotein

– Builds up as plaques in arteries causing heart attacks

– Hydrogenated oils & trans fatty acids are sources

• HDL: “Good” cholesterol– High-density Lipoprotein

– Removes LDL cholesterol

back to the liver

Organic Molecules: Proteins• Polymer of amino acids

• 20 amino acids– identical except for -R

group attached to central carbon

– amino acid properties determined by -R group

• The amino acids in a protein determine its structure and function

Amino Acids• Nonpolar -R

groups are hydrophobic

• Polar -R groups are hydrophilic

• Proteins contain many amino acids and are often amphiphilic

• -R groups determine shape of protein

Peptides

• A polymer of 2 or more amino acids• Named for the number of amino acids they

contain– dipeptides have 2, tripeptides have 3– oligopeptides have fewer than 10 to 15 – polypeptides have more than 15– proteins have more than 100

• Dehydration synthesis creates a peptide bond that joins amino acids

Dipeptide Synthesis

• Secondary structure– α helix (coiled), β-pleated sheet (folded) shapes held

together by hydrogen bonds between nearby groups

• Tertiary structure– interaction of large segments to each other and

surrounding water

• Quaternary structure– two or more separate polypeptide chains interacting

Protein Structure• Primary structure

– determined by amino acid sequence

Primary Structure of Insulin

• Composed of two polypeptide chains joined by disulfide bridges

• Frederick Sanger determined amino acid sequence (early 1950s).

• Contain a non-amino acid moiety called a prosthetic group

• Hemoglobin has 4 polypeptide chains, each chain has a complex iron containing ring called a heme moiety

Conjugated Proteins

Hemoglobin

Sickle Cell Anemia

• Caused by one different amino acid in hemoglobin

• Genetic• Pain in joints• No cure at present• Strangely Sickle Cell

raises resistance to Malaria

Protein Conformation and Denaturation

• Conformation - overall 3-D shape is crucial to function– important property of proteins is the ability to

change their conformation• opening and closing of cell membrane pores

• Denaturation– drastic conformational change that destroys

protein function• occurs with extreme heat or pH• often permanent

Enzymes• Function as catalysts

– promote rapid reaction rates

• Substrate - the substance an enzyme acts upon

• Naming convention– enzymes now named for their substrate with -ase

as the suffix• amylase enzyme digests starch (amylose)

• Lower activation energy – energy needed to get reaction started is lowered

• enzymes facilitate molecular interaction

Enzymes and Activation Energy

• Active sites– area on enzyme that attracts and binds a substrate

• Enzyme-substrate complex– temporarily changes a substrate’s conformation, promoting

reactions to occur

• Reusability of enzymes– enzymes are unchanged by reactions and repeat process

• Enzyme-substrate specificity– active site is specific for a particular substrate

• Effects of temperature and pH– change reaction rate by altering enzyme shape– optimum: temp = body temp, pH = location of enzyme

Enzyme Structure and Action

Enzymatic Reaction Steps

Metabolic Pathways• Chain of reactions, each catalyzed by an

enzyme • A B C D

– A is initial reactant, B+C are intermediates and D is the end product

, , represent enzymes

• Regulation of metabolic pathways– activation or deactivation of the enzymes in a

pathway regulates that pathway• end product D may inhibit or enzymes

Protein Functions• Structure

– collagen, keratin

• Communication– some hormones, cell receptors

• ligand - molecule that reversibly binds to a protein

• Membrane Transport– form channels, carriers (for solute

across membranes)

• Catalysis– enzymes are proteins

Protein Functions 2

• Recognition and protection– glycoprotein antigens, antibodies and clotting

proteins

• Movement– muscle contraction– cilia and flagella– spindle fibers

• Cell adhesion– proteins bind cells together

Nucleic Acids• The primary structure of proteins is

determined by genes – hereditary units that consist of DNA, a type of nucleic acid.

• There are two types of nucleic acid: 1. Deoxyribonucleic acid (DNA)

*Contains coded info that programs all cell activity.

*Contains directions for its own replication. *Copied and passed on from one generation to another. *In eukaryotic cells, it is found primarily in the nucleus.

Nucleic Acids

The second type of nucleic acid is:

2. Ribonucleic acid (RNA)

*Functions in the actual synthesis of proteins

coded for by DNA.

*Ribosomes – sites of protein synthesis.

*Messenger RNA (mRNA) – carries encoded

genetic message from nucleus to cytoplasm.

*Flow of genetic info: DNA →RNA →Protein

Nucleic acids are made from nucleotides

Each nucleotide consists of:1. A five carbon sugar;

2. A phosphate group attached to the number 5 carbon of the sugar; and

3. A nitrogenous base at C1

*There are two families of nitrogenous bases:

1. Pyrimidines

2. Purines

DNA

DNA is a polymer of nucleotides

joined by linkages between the

phosphate of one nucleotide

and the sugar of the next.

Variable nitrogenous bases

are added to this sugar-

phosphate backbone.

Watson and Crick – 3D Structure of DNA (1953)

• Two nucleotide chains wound as a double helix.• S-P backbones on outside of helix.• N bases paired in the interior of the helix and are

held together by H-bonds.• Base-pairing rules: guanine (G)-cytosine (C) and

thymine (T)-adenine (A).• Two strands of DNA are complementary – serve

as templates.• Most DNA molecules are long – thousands to

millions of base pairs each.

Model of DNA

DNA and RNA